[Openvpn-devel,2/2] crypto: move OpenSSL specific FIPS check to its backend

Message ID 20220126162830.20952-2-a@unstable.cc
State Changes Requested
Headers show
Series
  • [Openvpn-devel,1/2] crypto: move validation logic from cipher_get to cipher_valid
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Commit Message

Antonio Quartulli Jan. 26, 2022, 4:28 p.m.
Our crypto API already provides a function performing a validity check
on the specified ciphername. The OpenSSL counterpart also checks for the
cipher being FIPS-enabled.

This API is cipher_valid(). Extend it so that it can provide a reason
whenever the cipher is not valid and use it in crypto.c.

This way we move any OpenSSL specific bit to its own
backend and directly use the new cipher_valid_reason() API in the
generic code.

This patch fixes compilations with mbedTLS when some OpenSSL is also
installed. The issue was introduced with:
544330fe ("crypto: Fix OPENSSL_FIPS enabled builds")

Cc: David Sommerseth <davids@openvpn.net>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
---

NOTE: This patch makes "crypto.c: remove (dead) OpenSSL specific code"
obsolete.

Compiled with varoius libraries:
* Testing OpenSSL-1.0.2...
* OpenSSL-1.0.2 OK
* Testing OpenSSL-1.1.0...
* OpenSSL-1.1.0 OK
* Testing OpenSSL-1.1.1...
* OpenSSL-1.1.1 OK
* Testing OpenSSL-3.0.1...
* OpenSSL-3.0.1 OK
* Testing mbedtls-2.7.19...
* mbedtls-2.7.19 OK
* Testing mbedtls-2.10.0...
* mbedtls-2.10.0 OK
* Testing mbedtls-2.14.1...
* mbedtls-2.14.1 OK
* Testing mbedtls-2.16.11...
* mbedtls-2.16.11 OK
* Testing mbedtls-2.20.0...
* mbedtls-2.20.0 OK
* Testing mbedtls-2.26.0...
* mbedtls-2.26.0 OK
* Testing mbedtls-2.27.0...
* mbedtls-2.27.0 OK



 src/openvpn/crypto.c         | 11 +++--------
 src/openvpn/crypto_backend.h | 22 +++++++++++++++++++++-
 src/openvpn/crypto_mbedtls.c | 13 +++++++++----
 src/openvpn/crypto_openssl.c |  8 ++++++--
 4 files changed, 39 insertions(+), 15 deletions(-)

Comments

Antonio Quartulli Jan. 26, 2022, 9:09 p.m. | #1
Hi,

On 26/01/2022 17:28, Antonio Quartulli wrote:
> Our crypto API already provides a function performing a validity check

> on the specified ciphername. The OpenSSL counterpart also checks for the

> cipher being FIPS-enabled.

> 

> This API is cipher_valid(). Extend it so that it can provide a reason

> whenever the cipher is not valid and use it in crypto.c.

> 

> This way we move any OpenSSL specific bit to its own

> backend and directly use the new cipher_valid_reason() API in the

> generic code.

> 

> This patch fixes compilations with mbedTLS when some OpenSSL is also

> installed. The issue was introduced with:

> 544330fe ("crypto: Fix OPENSSL_FIPS enabled builds")

> 

> Cc: David Sommerseth <davids@openvpn.net>

> Signed-off-by: Antonio Quartulli <a@unstable.cc>

> ---

> 


FTR:

tested on RHEL8 with FIPS enabled and I couldn't experience any 
misbehaviou/crash while attempting to use a FIPS-disabled cipher.

Cheers,

-- 
Antonio Quartulli

Patch

diff --git a/src/openvpn/crypto.c b/src/openvpn/crypto.c
index 0aa76e05..b1303061 100644
--- a/src/openvpn/crypto.c
+++ b/src/openvpn/crypto.c
@@ -34,7 +34,6 @@ 
 #include "error.h"
 #include "integer.h"
 #include "platform.h"
-#include "openssl_compat.h"
 
 #include "memdbg.h"
 
@@ -1704,16 +1703,12 @@  print_cipher(const char *ciphername)
     {
         printf(", TLS client/server mode only");
     }
-#ifdef OPENSSL_FIPS
-    evp_cipher_type *cipher = EVP_CIPHER_fetch(NULL, ciphername, NULL);
 
-    if (FIPS_mode() && cipher
-        && !(EVP_CIPHER_flags(cipher) & EVP_CIPH_FLAG_FIPS))
+    const char *reason;
+    if (!cipher_valid_reason(ciphername, &reason))
     {
-        printf(", disabled by FIPS mode");
+        printf(", %s", reason);
     }
-    EVP_CIPHER_free(cipher);
-#endif
 
     printf(")\n");
 }
diff --git a/src/openvpn/crypto_backend.h b/src/openvpn/crypto_backend.h
index 7beaf9c3..e447036d 100644
--- a/src/openvpn/crypto_backend.h
+++ b/src/openvpn/crypto_backend.h
@@ -187,6 +187,21 @@  void cipher_des_encrypt_ecb(const unsigned char key[DES_KEY_LENGTH],
  */
 #define MAX_CIPHER_KEY_LENGTH 64
 
+/**
+ * Returns if the cipher is valid, based on the given cipher name and provides a
+ * reason if invalid.
+ *
+ * @param ciphername    Name of the cipher to check for validity (e.g.
+ *                      \c AES-128-CBC). Will be translated to the library name
+ *                      from the openvpn config name if needed.
+ * @param reason        Pointer where a static string indicating the reason
+ *                      for rejecting the cipher should be stored. It is set to
+ *                      NULL if the cipher is valid.
+ *
+ * @return              if the cipher is valid
+ */
+bool cipher_valid_reason(const char *ciphername, const char **reason);
+
 /**
  * Returns if the cipher is valid, based on the given cipher name.
  *
@@ -196,7 +211,12 @@  void cipher_des_encrypt_ecb(const unsigned char key[DES_KEY_LENGTH],
  *
  * @return              if the cipher is valid
  */
-bool cipher_valid(const char *ciphername);
+static inline bool cipher_valid(const char *ciphername)
+{
+    const char *reason;
+    return cipher_valid_reason(ciphername, &reason);
+}
+
 
 /**
  * Checks if the cipher is defined and is not the null (none) cipher
diff --git a/src/openvpn/crypto_mbedtls.c b/src/openvpn/crypto_mbedtls.c
index 01bfa020..a771777e 100644
--- a/src/openvpn/crypto_mbedtls.c
+++ b/src/openvpn/crypto_mbedtls.c
@@ -403,14 +403,17 @@  cipher_get(const char* ciphername)
 }
 
 bool
-cipher_valid(const char *ciphername)
+cipher_valid_reason(const char *ciphername, const char **reason)
 {
+    ASSERT(reason);
+
     const mbedtls_cipher_info_t *cipher = cipher_get(ciphername);
 
     if (NULL == cipher)
     {
         msg(D_LOW, "Cipher algorithm '%s' not found", ciphername);
-        return NULL;
+        *reason = "disabled because unknown";
+        return false;
     }
 
     if (cipher->key_bitlen/8 > MAX_CIPHER_KEY_LENGTH)
@@ -418,10 +421,12 @@  cipher_valid(const char *ciphername)
         msg(D_LOW, "Cipher algorithm '%s' uses a default key size (%d bytes) "
             "which is larger than " PACKAGE_NAME "'s current maximum key size "
             "(%d bytes)", ciphername, cipher->key_bitlen/8, MAX_CIPHER_KEY_LENGTH);
-        return NULL;
+        *reason = "disabled due to key size too large";
+        return false;
     }
 
-    return cipher != NULL;
+    *reason = NULL;
+    return true;
 }
 
 const char *
diff --git a/src/openvpn/crypto_openssl.c b/src/openvpn/crypto_openssl.c
index ea0147db..79afa4ab 100644
--- a/src/openvpn/crypto_openssl.c
+++ b/src/openvpn/crypto_openssl.c
@@ -571,12 +571,13 @@  cipher_get(const char *ciphername)
     return EVP_CIPHER_fetch(NULL, ciphername, NULL);
 }
 
-bool cipher_valid(const char *ciphername)
+bool cipher_valid_reason(const char *ciphername, const char **reason)
 {
     evp_cipher_type *cipher = cipher_get(ciphername);
     if (!cipher)
     {
         crypto_msg(D_LOW, "Cipher algorithm '%s' not found", ciphername);
+        *reason = "disabled because unknown";
         return false;
     }
 
@@ -588,6 +589,7 @@  bool cipher_valid(const char *ciphername)
     {
         msg(D_LOW, "Cipher algorithm '%s' is known by OpenSSL library but "
                     "currently disabled by running in FIPS mode.", ciphername);
+        *reason = "disabled by FIPS mode";
         return false;
     }
 #endif
@@ -597,11 +599,13 @@  bool cipher_valid(const char *ciphername)
             "which is larger than " PACKAGE_NAME "'s current maximum key size "
             "(%d bytes)", ciphername, EVP_CIPHER_key_length(cipher),
             MAX_CIPHER_KEY_LENGTH);
+        *reason = "disabled due to key size too large";
         return false;
     }
 
+    *reason = NULL;
     EVP_CIPHER_free(cipher);
-    return true;
+    return cipher;
 }
 
 bool cipher_var_key_size(const char *ciphername)